1. Technical Field
The present disclosure relates to a method and apparatus for treating an intervertebral disc for relief of back pain. More particularly, the present disclosure relates to a method and an apparatus for measuring pressure of an intervertebral disc during heating.
2. Description of Related Art
The curing of back pain is one of the most important objectives of neurosurgeons, orthopedists, anesthesiologists and neurologists. Back pain is one of the most common forms of pain and accounts for huge amounts of disability and loss of labor throughout the world. The curing of back pain heretofore has been in the domain of surgery, percutaneous injection of chemicals into the intervertebral disc, percutaneous removal by mechanical means of intervertebral discs, RF heating of peripheral nerves outside of the intervertebral disc to interrupt nerve fibers outside of the disc, and various forms of drug and rehabilitation therapy.
The use of radiofrequency (RF) electrodes and power sources for generators is common in the field of neurosurgery, anesthesiology, and cardiology for the destruction of neural tissue. This is typified by the RF electrodes and RF lesion generator systems of Integra Radionics, Inc. in Burlington, Mass., USA. Heretofore, the lesion electrodes are placed at the target site under various types of guidance, including stimulation, x-ray control, tomographic image control, and stereotactic apparatus. The electrode typically consists of an insulated shaft with an exposed tip which is elevated to radiofrequency potential. A second electrode, usually a dispersive electrode with a large area, is placed elsewhere on the body to return the radiofrequency current to the RF generator, thereby making the patient's body part of the radiofrequency circuit. The intensity of radiofrequency current at the exposed tip of the radiofrequency lesion electrode causes the heating of the tissue in the neighborhood of the electrode, and thus the destruction of that tissue. Typically, the tissue has always been either direct neurological tissue, such as in the brain or the spinal cord, or muscle tissue, as in the heart in the case of cardiac ablation.
A typical example of radiofrequency lesion making is for the relief of various types of back pain, as in the case of facet denervation or in direct destruction of low back nerve structures such as the sympathetic nerves or communicating rami. In the case of facet denervation, the electrode is placed near a small nerve branch which innervates the spinal facet joints and a heat lesion is made which interrupts the noxious signals emanating from these joints. RF heating is also used for destruction of ganglia such as the sphenopalatine ganglion or of other nerves which are ramifications of the nerves which exit from the spinal column. The mechanism is a direct interruption of nerves and thus of the pain signals from the affected areas to the spinal cord. These procedures have been effective; however, there are many pain syndromes which relate to the region around the intervertebral disc itself. It is very difficult to achieve a comprehensive destruction of the nerves which innervate the disc. This is because the disc is innervated by multiple nerve branches. Some of these branches lie close to the exiting spinal nerves, notably those which innervate the clinically important posterior part of the disc. Destruction of these branches with a heat lesion would therefore carry the risk of damaging the spinal nerves. It would be a very effective treatment for so-called discogenic back pain to be able to simply and with a minimal number of percutaneous needle sticks denervate or destroy the numerous nerve structures which are present at the surface of the entire disc without endangering the important nerve structures inside and exiting from the spinal canal.
It has been a characteristic of RF lesion making in the nervous tissue or in the soft muscle tissue that the RF electrode, which affects the heating, be placed in proximity to the tissue to be destroyed. That is, by various stereotactic means such as X-ray, fluoroscopy, computerized tomography (CT) guidance, magnetic resonance (MR) guidance, or stimulation and recording, the tip of the RF electrode is placed directly on or very near the target nerves themselves and the heating is subsequently carried out.
As alluded to above, one of the outstanding problems in the treatment of back pain relates to neural structures that innervate the intervertebral disc itself. There are numerous sensory nerves which cluster at the exterior surface of the intervertebral disc and sense mechanical deformations of the disc. These nerves appear to protect against excessive stress of the disc wall, which in turn may cause serious damage to the disc, such as rupture, bulging, or herniation. In the situation of an overstressed disc, a rupture can cause extrusion or bulging of the inner material of the disc beyond the external wall with consequent pressure on nerves in the vicinity. This is one of the most common forms of back pain and usually must be cured by surgery or percutaneous disc removal. However, another very common form of back pain related to the disc is the mere irritation or stimulation of the numerous small nerves that innervate the periphery of the disc and sense its mechanical stress. These nerves are found ubiquitously over the surface of the disc. In the situation where herniation or extrusion of the disc has not taken place, yet these numerous tiny nerves are stimulated to produce a painful response, there is no simple surgical treatment and the patient may be in extreme pain and distress as a result. It may be fruitless to attempt to place an RF electrode directly on these small nerves, as they are distributed over an extensive surface of the disc, making it impractical and dangerous to introduce a sufficient number of electrodes in to denervate all of them. More particularly, it is not possible to know beforehand exactly which of these sensing nerves is causing the problem. Indeed, there may be a large number of them over the entire surface of the disc in the situation that the disc is extremely distorted, or alternatively, only a subset of them at one particular location for a more focal disc bulge.
U.S. Pat. No. 5,433,739 issued to Sluitjer et al. on Jul. 18, 1995 describes a technique of introducing an RF electrode or other heating electrode into the intervertebral disc, typically under fluoroscopic control, and heating the entire disc to a temperature significantly above body temperature. The heated disc heats the nerves which innervate its surface, and the nerves are destroyed or altered when the heat of the disc is elevated to an appropriately high temperature. The nerves are heated and desensitized around the disc by minimal invasion to the body, while at the same time sparing the larger nerve bundles running in the vicinity of the disc. This technique produces significant pain relief in a substantial fraction of patients suffering from back pain. Additionally, an indirect radiofrequency lesion method is described whereby the destruction of desired neural structures is done not by direct placement of an RF electrode near the structures, but rather by the radiofrequency heating of an intermediate structure, which in turn diffuses the heat to the neural structures in a more diffuse and global fashion.
Associated with indirect or global radiofrequency heating techniques, it is important to be able to monitor pressure, not only at the direct point of RF electrode heating, but also at remote points in space so as to monitor and control the progress of decreased tissue volume. Thus, there remains a need to provide intervertebral pressure monitoring systems to carry out the direct and/or indirect monitoring of points in space relative to the primary RF lesion electrode for safer and more effective control of the heating process.